On March 26, 1351, in the Duchy of Brittany in western France, two teams of knights, squires and men-at-arms faced off across a field midway between Josselin and Ploërmel castles. Though it was springtime and far from the dog days of summer, sweat streamed down the faces of those assembled. From either side men clad in 30 pounds of armor took the measure of their opposition in anticipation of the coming engagement.
Jean de Beaumanoir, the French governor of Josselin Castle and champion of the House of Blois claim to Brittany, strode out to midfield to formally challenge his rival, Sir Robert Bemborough, the English captain of Ploërmel castle and champion of the House of Montfort claim to the duchy. Each had mustered 30 men on this predetermined day to give battle in what would become known as the Combat of the Thirty. Its outcome would not settle the ongoing War of the Breton Succession but was a question of chivalric honor.
The War of the Breton Succession erupted in 1341 after John III, Duke of Brittany, died that April 30 without an heir, but after having named rival successors to his ducal title. One was his niece, Jeanne de Penthièvre, wife of Charles of Blois, the latter a nephew of French King Philip VI. The other was his formerly estranged younger half brother, John de Montfort. With a mercenary army to back him, Montfort gained the support, or at least submission, of the principal Breton towns, as well as control of the ducal treasury. While an assembly of townspeople and minor nobles recognized him as duke that May, he enjoyed only marginal acceptance among the upper nobility.